Dieback of poplar and willow caused by Pseudomonas syringae in combination with freezing stress

Abstract

Abstract Dieback of poplar and willow, grown in short‐rotation forestry plantations, was shown to be a result of Pseudomonas syringae infections in combination with freezing stress. Bacteria isolated from damaged poplar and willow trees at several sites in Sweden, identified as P. syringae , showed ice nucleationactive (INA) properties in laboratory tests. To confirm the effect of bacterial infection, five different P. syringae isolates were reinoculatcd into stems of Salix viminalis, S. dasyclados and Populus spp. in the greenhouse before application of sub‐zero temperature stress. Subsequent dieback of the shoots was observed. It is concluded that P. syringae is a Potentiall severe pathogen of willow and poplar.